1. Field of the Invention
This invention relates to building wall structures and, more particularly, to dry sealed, flat metal plate exterior wall panel systems used in curtain wall construction. The metal plate is most commonly made of painted aluminum but can be made of painted steel or stainless steel.
2. Description of the Prior Art
Aluminum wall plate panels have been widely used in curtain wall construction. There are two major categories of the metal plate curtain wall systems; namely, a wet sealed system, and a dry sealed syetem. In the wet sealed system, exposed caulking is applied along the vertical and horizontal joints between panels to form a weather-tight exterior wall surface. In the dry sealed system, it is required that practically all sealants, such as gaskets or sealants, be concealed from exterior viewing except smll areas, such as the spliced joint or four corner intersection. Only the prior art dry sealed system which relates to the present invention will be discussed below.
The individual plate panel consists of an exterior flat metal plate and four perimeter members structurally connected to the plate using structural adhesive, connecting clips, welded studs, or the combinations thereof. The thickness of the metal plate normally ranges from 0.06 inches (1.524 mm) to 0.25 inches (6.35 mm). The width of the plate normally ranges from 1 foot (0.3048 m) to 5 feet (1.524 m). The length of the plate normally ranges from 3 feet (0.9144 m) to 20 feet (6.069 m). The perimeter members are normally made of extruded aluminum. Depending on the design wind load intensity and the plate size, intermediate plate stiffening members may be required. At least one of the perimeter members is securely fastened to the wall panel supports. Under wind load condition, the load on the wall panel surface is transmitted to the perimeter members into the wall supports.
In addition to the load resisting requirement, the performance requirements of a dry sealed flat metal plate exterior wall panel system include the following items:
a. To retain the flat appearance of the plate, the plate shall be designed to move relatively free in relation to the perimeter members in the case of thermal expansion or contraction. To accomplish this goal, several methods have been used to connect the plate to the perimeter members, such as using flexible structural adhesive (e.g.--silicone), slidable clips, welded studs on the plate with an oversized hole on the perimeter member, or the combination thereof.
b. To prevent panel bowing under therml expansion condition, the perimeter member shall be designed to move relatively free in relation to the wall supports. To accomplish this goal, elongated holes on the connecting member are normally provided around the fasteners, such as metal screws or bolts. The problem caused by the elongated holes is due to the following two conflicting functional requirements. For resisting the wind load normal to the wall surface, it is desirable to install the fasteners as tight as possible, while for allowance of thermal movements, it is desirable to install the fasteners as loose as possible. Weighing the two functional requiremnts, it is difficult, if not impossible, to have an optimal field control in installing the fasteners. In addition, prepunching the elongated holes in the shop will severly limit the ability to absorb the erection tolerance in the field concerning the location and alignment of the wall supports, while making the elongated holes in the field is time consuming and difficult.
c. To limit the air and water infiltration, the panel joints must be sealed in a concealed location. Shop applied perimeter sealant using either caulking or gasket has been utilized to seal off the gap between the plate and the perimeter members. To accomplish the goal of concealed sealant, the panel joints are formed by engaging a male spline into a female groove, whereby the sealant is hidden within the female groove and the exposed part of the male spline becomes the exposed panel joint surface. The male spline is normally served as a structural component to transfer the load from the female side perimeter member into the male side perimeter member. The male spline is normlly either an integral part of the perimeter member or securely fastened to the perimeter member. Panels are engaged both horizontally and vertically in the same manner. The problems with the construction includes the following items:
1. The erection can be performed in a single direction only, either from left to right, or from right to left. PA0 2. It is difficult to erect a bent corner panel. PA0 3. If the wall surface is wrapped around a building, it is difficult to install the last panel around each course. PA0 4. It is difficult, if not impossible, to replace an individual damged panel after the completion of the wall construction.
d. The wall system must be designed to drain out the water due to backside condensation and possible leakage through the panel joints. To accomplish this goal, an internal horizontal gutter is built in the top perimeter member to collect the condensation and leakage water for drainage toward outside. The gutters are spliced across the vertical panel joints to make them continuous. Two methods of gutter drainage have been known in the art. The first method is to provide exposed weep holes near the bottom of the gutter. The second method is to provide internal vertical drainage channels to allow the water to drain from the top gutter to the gutter below and eventually to the bottom gutter at the wall base or window head where exposed weep holes are provided to drain the water to the exterior. The problems with the first method include the following items: (1) Under a positive pressure difference (i.e., exterior pressure being greater than the interior pressure), the water will continue to flow into the internal gutter through the weep holes until the water head in the gutter is adequate to counterbalance the pressure difference. Therefore, no matter whether the panel joints leak or not, a significant amount of water will be accumulated in the internal gutter. Thus, the first defense against the water leakage is solely relied on the integrity of the gutter spliced joint and the use of the internal gutter system as a second line of defense against water leakage becomes a pure illusion only; (2) When air penetrates through the weep holes, it creates a bubbling phenomenon in the water within the gutter and causes the water to splash over the gutter leg producing the uncontrolled water leakage condition. To prevent the water splashing problem, normally porous baffle material is installed at the weep hole location. However, when the baffle is totally submerged in the water, it becomes ineffective. The alternative is to use a higher gutter leg or a separate shielding plate which increases the cost of the system; (3) The exposed weep holes are unsightly and may create water stains on the wall surface under the weep holes; (4) The workmanship of the field-installed gutter spliced joint is critical to the successful function of the design. The problems with the second method of gutter drainage include the following items: (1) The water due to condensation and possible joint leakage is accumulated at the bottom gutter for drainage. For a high wall construction, the volume of expected water at the bottom is difficult to calculate and thus, is difficult to design for proper drainage; (2) The required gutter capacity varies from level to level. Using the maximum required gutter capacity for the design of the top perimeter member is uneconomical. Using different design for different level is costly and ipractical for mass production.